Protective device



E. E. F. CREIGHTON.

PROTECTIVE DEVICE.

APPLICATION FILED MAR. 9, 1917.

1,374,826. Patented Apr. 12, 1921.

Inventor": Elm er ELFYCvei hton,

9W I His orrwes.

UNITED STATES5 PATENT OFFICE.

ELMER E. F. 'CREIGHTON, SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

raorncrrvn DEVICE.

Specification otietters Patent.

Patented Apr. 12, 1921'.

Application filed Kai-ch 9, 1917. Serial No. 153,751.

phone orsimilar lines of communication in parallel to transmission lines, onoverhead systems such telephone and transmission lines being often carried on the same poles and in cable'systems such lines being closely paralleled in the ground. In either case, such telephone lines are often put entirely out of order and rendered unfit for use, through the inductive effect of the parallel transmission lines. causes heavy induced currents to exist on, the telephone lines, arcing over arrester and preventing any transmission of into ligence. The current induced in telephone lines which parallel transmission lines may be due to the occurrence thereon of certain abnormal conditions occasioned by conditions of accidental ,groundin in such a manner as to cause heavy earti currents to be set up. It is well known practice to protect transmission systems from the occurrence thereon of accidental grounds by means of a ground protecting device, such a device being known in the art as an arc- 4O, ing ground suppressor. The arcing ground suppressor operates to close a path to ground in shunt to the accidental or arcing ground causing, thereby, a sufficient drop in potential on the grounded conductor to extinguish or remove the arcing ground. Considering transmission lines of non-grounded neutral systems or systems in which the neutral is grounded through a high resistance, the only current which can flow to ground when the arcing ground suppressor operates in response to an accidental ground, is the well known electrostatic charging current, which has no detrimental inductive efiect on parallel telephone lines. If, however, conditions occur in which a short circuit cur- It iswell known practice to operate tele This inductive. eifect' rent fiow's to ground, then the operation of the arcing ground suppressor sets up a condition in which a portion of the heavy short circuit current returns to the generator through the round and the suppressor, producmg there y heavy induced currents in surrounding telephone lines.

By my invention, I am able to protect telephone and similar lines from the results of such inductive interferenceb'} a controjlling means associated with the arcing ground suppressor or similar device whi h is .operative to allow the o eration of t e suppressor on conditions w ere its opert1on producesno inductive effect on parallel telephone lines but to hold the suppres-- sor inoperative on conditions when its operatlon would lnduce heavy currents in such telephone lines.

The novel features which I believe tobe characteristic of my invention will bevdefinitely lndicated in the appended claims while the features of construction and mode of operation will be understood 'by reference to the following description taken in connecshows the preferred embodlments of, my invention and in which the figure is a diation with the accompanyin drawing which? shown, for purposes of illustration, a three phasetransmission line which may be-either of the overhead or cable ty e comprising three conductors 1, 2 and 3. or rotecting th1s line from accidental .groun s, I have shown a ground protecting device, which by way of'illustration is an arcing ground suppressor of the type shown anddescribed in an articl written by me and published in the A. I. E. Proceedings for 1911, page 377. For purposes of clearness, I have omitted some of the details of construction of this device and only a brief description the electrostatic type and comprising a normally balanced armature member 11 cooperating with fixed contacts 12 corresponding to each conductor. The armature or movable contact member 11 of the relay is operative upon unbalancing, due to the reduction of voltage on any conductor caused by an accidental ground thereon, to engage the contact 12 corresponding to the faulty conductor, and thus close the operating circuit of the switch corresponding to the faulty conductor. The relay 10, therefore, selectively controls the operation of each of the switches 4, 5. and 6 which close their respec- 1'5 tive paths to ground to form a low resistance path in shunt to the accidental ground. The operating circuit for the arcing ground suppressor comprises, therefore, a source of current 13 connected to the movable member 11 of the relay and then by contacts 12 and conductors 14, 15 and 16 .in parallel, to the operating mechanisms of the switches 4, 5 and 6, respectively, and thence by means of the common return conductor 17 back to the source of current 13.- The operation of the relay 10, therefore, closes the operating circuit for the suppressor through one of the parallel circuits which correspond to the faulty conductor and its respective switch is operated to remove the arcing ground by dead grounding the faulty conductor and reducing the voltage at the accidental ground to a valueinsuflicient to maintain the accidental ground whereupon the switch is 86 adapted to automatically open the dead ground connection to restore the conductor to its normal condition. It is understood that my invention is not limited in its application to the specific type of arcing ground suppressor described but is applicable to control the operating circuit of any type of ground suppressor.

Associated with the operating circuit of the ground protecting means, I have provided my control device comprising a movable contact member or armature 18 cooperating with a fixed contact member 19 to open or close the operating circuit of the ground protecting means or arcing ground suppressor, under certain conditions, this circuit being controlled by the members 18 and 19 of my control device and the contacts of the relay 10 in series. Members 18 and 19 are normally held in circuit closing 56 position by means of a member or spring 20 operatively related to the armature member 18. For moving the member 18 to circuit opening position, I have provided an electromagnetic means comprising three 60 windings 21, 22, 23 wound on a common core 24 and connected to secondaries 25, 26, 27, respectively, of current transformers which are connected to conductors 1, 2 and 3, respectively. One of the windings is reversed relatively to the other two, for instance winding 23, in order to provide a constant pull on the armature member 18. This electromagnetic means is so arranged that under certain conditions the pull exerted on the armature member 18 is sutficient to move the member into circuit opening position against the pull of spring 20 while under other conditions the armature member 18 is maintained in circuit closing position.

When an accidental ground occurs on any conductor of the system shown, such as conductor 8, for instance at 28, the arcing ground suppressor operates, as described, to dead ground the-conductor and during the occurrence of the accidental ground and when the suppressor is operating, the only current which can flow to ground is the electrostatic charging current which flows to ground and returns to the generator by means of the earth connection. Such current is not enough to cause any material induction in parallel telephone lines and is not considered therefore detrimental. Under such conditions, it is essential that the arcing ground suppressor, operate to remove, if possible, the accidental ground from the system. Under these conditions, therefore, my control device is inoperative, as under normal conditions and under conditions of a ground on one conductor not enough current flows-through the coils 21, 22,23 to attract the armature member 18 and it remains in engagement with contact 19 and therefore in circuit closing position. The operating circuitof the ground suppressor is therefore closed by my control device and is only open at the phase selecting relay 10. When, therefore, such an acci dental ground occurs, the member 11 of relay 10 operates to engage the contact 12 corresponding to conductor 3 and, the operating circuit for switch 6 is closed from the source of current 13 through members 19' and 18 of my control device along conductor 17 to the operating mechanism of switch 6, thence along conductor 16 to the contact 12 closed by the relay and through the member 11 back to the source of current 13. As before stated, the switch 6 is thereupon operated to connect the conductor to ground through conductor 9 and thus form a grounded path in shunt to the accidental ground which acts to reduce the voltage sufficiently at the accidental ground to remove it and the phase selective relay 10 then opens the operating circuit of switch 6 and the system is restored to normal condition.

Under other abnormal conditions, we may have a short circuit current flowing to ground, such a condition existing when a short circuit occurs between two conductors such as conductors 2 and 3 at 29 for instance which may be of a character to also are to ground from one of those short circuited conductors such as conductor 3 at 28 for instance.

.the generator throu h the Such a condition is most likely to occur in a transmission system of the cable type and we have the condition of botha short circuit and a ground occurring on the system. Under these conditions if the ground protecting means were permitted to operate, the relay 10 would operate and switch 6 would be actuated to close the path to ground from conductor 3 along the conductor 9. The entire short circuit current would then tend to flow back along conductor 3 but since there is an appreciable resistance in the conductor there will be a division of the short circuit current, a portion returning to the generaor over conductor 3 and a portion through the earth and back to conductor 3 through the path of conductor 9 closed by switch 6, ac-

cording to'thefelative conductances of the The short circuit current intwo circuits. passing through the ground to the generator will form a loop, out the conductor 2 across the short circuit 29 through the accidental ground 28 and through, the ground back to switch 6 and the conductor 9. This eavy suflicient to maintain a persistent arc to ground in spite of the ground protecting means and will induce a very heavy current in parallel telephone lines which is not only dangerous but which will put the communicating apparatus out of commission.

When, therefore, such a condition occurs the operation of the ground protecting means, cannot remove the ground and there is, therefore, no need of its operation as the grounding of the system in an effort to extinguish the accidental ground only sets up conditions which. are extremely detrimental to telephone lines. Under such conditions, my control device is operative to prevent the operation of the sup as due to the heavy current through t e coils 21, 22 and 23 the armature member 18 is attracted against the action of spring 20 and disengages with control member 19 to open the operating circuit of the ground suppressor and remain in circuit opening position. The operation, therefore, of the relay 10 is ineffective to operate the switches 4, 5 and 6 as my control device is arra ed to operate prior to the operation of the re ay 10. When this short circuited condition is removed, the pull exerted on the armature member 18 is reduced so that the spring 20 returns the control device to circuit closing position again.-

It is thus a parent that my control device operates to istinguish between conditions occurrin on a which t e ground protecting means operates with or without detriment to parallel telephone lines. My device operates to hold the arcing ground suppressor inoperative under conditions'where its 0 eration would cause heavy inductive inter erence inparcurrent would be ressor,

transmission line under lar lines which parallel transmission lines without impairing the protection of the system itself.

My invention may be embodied in other forms than that shown and described and I, therefore, do not wish to be restricted to the precise construction shown but intend to cover by the appended claims all changes and modifications which are within the scope of my invention and which will be apparent to those skilled in the art.

What I claim as new and desire to secure by Letters Patent of the United States, is,- 1. The combination with an electric transmission line, of an arcing ground suppressor, a control circuit therefor, and means operative inresponse to an arcin accompanied by short circuit condltions between phases to render said control circuit inoperative. l 2. The combination with an electric trans mission line, of an arcing ground suppressor, and an electro-responsive device controlling said suppressor to permit its op-.

eration under conditions of accidental ground on said line but to prevent its operation when said accidental ground is accompanied by conditions of short circuit.

3. In combination with the conductors of a transmission line, normally open grounding circuits for said conductors, switching means adapted to be selectively operated to close said groundin circuits, a relay connected to said con uctors arranged selectively to control circuits tending to operate said switching means whenever a ground occurs on one of said conductors to dead ground the same, and an electroresponsive device having windings connected to carry currents proportional to the currents in said conductors cooperatively related to said relay to prevent operation of said switching means when thereis a short circuit on said line. i

4. The combination with an electric transmission line, of an arcing ground suppressor including an operating relaytherefor, and an electroma netic device operative in responsive to con itionsof short circuit on said line to render said relay inefiective to operate said su pressor.

5. The combination with an electric transmission line, of 'means associated therewith and operative in response to the occurrence of an accidental ground on said line to provide a path to ground in shunt to said accidental ground, and means operative in response to the occurrence of an arcing ground accompanied by a short circuit for rendering said first mentioned means inoperative.

6. The combination with an electric transground mission line, of an arcing ground suppres 801', including an operating relay therefor, a control circuit controlled by said relay, contact members included in said control circuit normally held in circuit closing position, and means for moving said contact members to circuit opening position prior to the operation of said relay in response to the occurrence of a short circuit on said line.

ing said control circuit open independent of said means under predetermined abnormal conditions.

8. The combination with the conductors of an electric transmission line, normally open paths to ground from said conductor, switches controlling the closing of said paths,' a control circuit for said switches,

means for closing said control circuit to selectively actuate said switches in response to the occurrence of accidental grounds on their respective conductors, and a second means operative in response to predetermined abnormal conditions on said line for independently opening said control circuit whereby the subsequent closing of said circuit by said first mentioned means is ineffective. 4

9. A protective system comprising a polyphase transmission line, grounding means adapted to be operated to dead ground selectively the conductors of said line, a relay connected to said conductors normally operative in response to grounds on said conductors to control the operation of said grounding means, and an electro-responsive device provided with windings connected in circuit with said conductors operative in response to short circuits between phases of said line to prevent the actuation of said grounding means.

In witness whereof, I have hereunto set my hand this 8th day of March, 1917.

ELMER E. F. 'CREIGHTON. 

